This invention is in the field of air conditioning by refrigeration and in particular to the control of the level of humidity independently of the temperature, while using fresh, return or ambient air from the controlled space to preventing over cooling. The invention provides independent humidity control while preserving as much heat as possible from the inlet air thus limiting sensible cooling relative to latent cooling without using expensive reheat or additional coils.
Air conditioning and controls for adjusting the air-conditioning equipment, to achieve a desired comfort zone by controlling the temperature and humidity levels, are well known. Such devices are shown in numerous patents described below. Any such air conditioning system typically uses a chilled fluid or a circulating refrigerant in a heat exchanger coil as a conditioning means to cool and dehumidify air before it is forced into an indoor controlled space. The rate of cooling provided by some systems of this kind, such as chilled fluid systems, is varied in response to a thermostat placed within the indoor space being cooled, with variations occurring in a smooth manner to maintain a chosen temperature level at the thermostat. In other systems, such as split-systems and package units, the air conditioning system compressor turns on and off in response to the thermostat. In recent years, some manufacturers have incorporated humidity sensing into their controls. Humidity control has typically been accomplished through adjustment of the temperature set point or calculation of a comfort condition based on a combined temperature-humidity setting, rather than through a control strategy based on user selectable separate temperature and humidity set points.
It has long been recognized that proper air conditioning systems should not only lower the temperature of the interior space being served when the temperature therein has exceeded a predetermined level but should also control the relative humidity of the space as a function of the air conditioning. During operation of a typical air conditioning system, air from the space to be conditioned is circulated over a heat exchanger. The heat exchanger absorbs heat energy from the air lowering its dry bulb temperature. If the temperature of the air is lowered below its dew point, then moisture from the air is condensed onto the heat exchanger surfaces and the actual amount of moisture contained in the air is reduced.
Most air conditioning systems provide dehumidification passively as a byproduct of cooling. In most systems, the amount of dehumidification delivered by the system is not sensed, controlled, or responsive to the user""s needs. Most currently available systems control the amount of cooling delivered by the heat exchanger coil, but not the amount of dehumidification. The space temperature or temperature of a room for example, is maintained within a few degrees of the user""s setting, however, the space humidity typically swings up and down, as temperature varies. At times of low load and humid conditions, this swing in humidity can be plus or minus 20% rh resulting in space humidity levels that exceed the maximum comfort levels of 60-70% rh recommended by ASHRAE (American Society of Heating Air-Conditioning and Refrigeration Engineers). Supply duct humidity typically exceeds 90% rh in such systems. The maximum recommended humidity level for supply ducts is 70% rh to prevent fungal growth. These recommended humidity levels are independent of temperature. Present-day air-conditioning system""s have not adequately addressed these problems. Excessive energy consumption, complexity, expense, coil freezing, and/or premature compressor failure have confined the practicality of systems that claim to address these problems to specialized applications.
One such system shown in U.S. Pat. No. 5,802,862, which describes a combined, reheat coil runaround system. U.S. Pat. Nos. 4,350,023 and 4,448,597 describe a control scheme for a reheat apparatus that has an additional coil located downstream of the evaporator coil, referred to as a sub-condenser. A similar arrangement is described in U.S. Pat. No. 4,182,133, which uses one coil with multiple circuits, and in U.S. Pat. No. 5,622,057. One of the earliest examples of reheat is described in U.S. Pat. No. 2,451,385, with a variation described in U.S. Pat. No. 2,685,433, in which first cooling and then heating are sequentially provided through separate air streams. By its very nature, heating air after considerable energy has been expended to cool said air is wasteful and results in significantly increased energy expense. The additional heat exchanger coils that are required make such systems expensive to install and more difficult to maintain.
Reheat can be provided with no additional energy expense by exchanging heat from the air entering the coiling coil to the air exiting the cooling coil, as described in U.S. Pat. No. 4,428,205. A current example of this technology is wrap around heat pipes, which significantly increase equipment cost.
U.S. Pat. No. 4,984,433 describes an air conditioning system with a variable sensible heat ratio. The system includes a variable speed supply air fan and a plurality of subcooling coils. The controller senses temperature and humidity and tracks their change over time to predict if the latent and sensible needs will be satisfied simultaneously. When it is desired to remove more latent heat than sensible heat, the supply air fan speed is reduced and subcoolers are activated. This system requires expensive components including a variable speed fan and additional refrigerant coils and solenoids. As with previous inventions of this type, energy waste and the problems of coil freezing and liquid entering the compressor are not solved.
U.S. Pat. No. 3,938,348 describes a unit in which an evaporator coil is maintained at a selected cool or dew point temperature constantly, regardless of whether cooling is required. The compressor is turned on and off, or it is a two-speed, or two compressors are used to constantly maintain the evaporator at a selected temperature. U.S. Pat. No. 5,346,127 describes an air handler arrangement where air flow through the coil is varied, according to the sensible load, via face and bypass dampers.
U.S. Pat. No. 4,485,642 describes a heat exchanger air bypass for humidity control by a manually set damper apportioning the air flowing through the heat exchanger and bypassing the heat exchanger. U.S. Pat. No. 5,303,561 describes a controller that produces a slower fan speed when conditions are humid, based on temperature and humidity sensors. The system modulates the indoor fan speed to attempt to stay within the comfort envelope defined by combined relative humidity and temperature measurements. Other examples are disclosed in U.S. Pat. No. 2,236,058 which describes a variable speed fan; U.S. Pat. No. 2,296,530 which describes a face damper only; U.S. Pat. Nos. 2,685,433; 3,251,196 which describes three staged fans; and U.S. Pat. No. 4,003,729 which, describes a variable speed fan in conjunction with a coil temperature sensor. U.S. Pat. No. 5,346,129 describes a controller that starts a condensing unit in response to an error signal that is a combination of temperature and humidity. Another combined controller is described as in U.S. Pat. No. 5,850,968, which is a comfort controller replacement for a conventional thermostat.
U.S. Pat. No. 4,105,063 discloses an air conditioning system with a sensor responsive to a predetermined maximum moisture content, operated in parallel with the normal dry-bulb temperature control. U.S. Pat. No. 4,889,280 discloses an auctioning controller wherein the predetermined dry-bulb temperature set point is modified in response to an absolute humidity error signal. Another controller is described in U.S. Pat No. 5,195,473, which operates a system having an HVAC control and a humidity limiting control.
According to the inventive principles as disclosed in connection with the preferred embodiment, what is shown and described is an air conditioning system and method, including a controller which varies the sensible capacity in relation to the latent capacity to achieve humidity reduction in such a manner as to satisfy separate user selectable temperature and humidity conditions while minimizing the energy consumption of the air conditioning process. At full enhancement, the present invention provides a 64 percent increase in dehumidification capacity over conventional systems, and a concurrent decrease in temperature reduction capacity reduces overcooling and decreases or eliminates the need for expensive reheat. The inventive principles disclosed are comprise an independent humidity setting that controls the level of dehumidification, separation of outside air, ambient and return air at the inlet, a bypass that preserves ambient heat and minimizes use of reheat, and a controller that maximizes energy efficiency.
The system is arranged, according to the inventive principles as disclosed in connection with the preferred embodiment, to prevent freezing of the air conditioning refrigeration equipment and to prevent liquid refrigerant from entering the compressor. More particularly, dehumidification efficiency is achieved according to the inventive principles as disclosed in connection with the preferred embodiment, by using the air flow directing means, such as ducting as would be known to one skilled in the art, and directing a part of the flow of return air from the controlled space or the ambient air, through a bypass which serves to direct the air to a mixing chamber and bypassing the heat exchanger. As would be understood by one skilled in the art, ambient air, according to the inventive principles as disclosed in connection with the preferred embodiment, is from the controlled space. According to the disclosed inventive principles, the bypassed air may be from a source other than the space in which the relative humidity is to be controlled and may include admix of air from other sources or may be ambient air from the controlled space and air from another source. An achievement of the invention is the ability to dehumidify a controlled space responsive to an independent relative humidity indication or signal, separate from a temperature responsive indication or signal. The portion of the ambient air not directed through the bypass, is directed by the airflow directing means or ducting, as would be known to one skilled in the art, to the heat exchanger where the ambient air flow is cooled by its passage through the heat exchanger and then to the mixing chamber where it is mixed with the bypassed air directed through the bypass. According to the inventive principles as disclosed in connection with the preferred embodiment, the part of the ambient air flow directed through the heat exchanger may be mixed with another source of air, such as an outside air flow. If outside air is to be introduced, in the preferred embodiment an adjustable partition divides the intake plenum to separate outside air from ambient air so that mixing does not take place prior to entering the bypass and the heat exchanger. According to the inventive principles as disclosed in connection with the preferred embodiment, the ambient directed to the heat exchanger and the outside air flow directed to the heat exchanger, are divided, until the separate air flows pass the heat exchanger. In this way greater efficiencies are achieved. The mixing chamber of the airflow directing means receives the air from the bypass and the heat exchanger, where mixing occurs and the mixed air is discharged into the controlled space where it is mixed with the space air. As stated, according to the inventive principles as disclosed in connection with the preferred embodiment, by outside air is intended air from a source other than the controlled space ambient and may be two or more such sources separately directed; to said air directing means or mixed in any suitable manner.
The operation of the dehumidification, according to the inventive principles as disclosed in connection with the preferred embodiment, is responsive to an active humidity signal from a controller having a humidity sensor in the ambient air. The controller, as would be known to one skilled in the art, may produce discrete or continuous humidity active or inactive signals, as would be known to one skilled in the art. According to the inventive principles as disclosed in connection with the preferred embodiment, the dehumidification mode operates according to a separate active humidity signal independent of temperature variations or an active temperature signal. In such cases where the temperature of the ambient is reduced below a differential temperature setting and an active humidity signal exists, a heating means may be used to reheat the airflow from the mixing chamber or the bypass of the air directing means. However, as would be known to one skilled in the art, the dehumidifier operating according to the inventive principles as disclosed in connection with the preferred embodiment, provides dehumidification responsive to a separate active humidity signal and independent of the sensed ambient temperature.
Freezing of the condensate on the heat exchanger may be prevented, according to the inventive principles as disclosed in connection with the preferred embodiment, by a temperature sensor responding to the heat exchanger temperature. The controller, responsive to the heat exchanger temperature would then be used to regulate the operation of the bypass regulation means and/or the heat exchanger to raise its temperature, bringing it above the freezing point. Passage of liquid refrigerant into the compressor may be prevented, according to the inventive principles as disclosed in connection with the preferred embodiment, by use of a thermostatic expansion valve in the high pressure refrigerant circuit, made responsive to a the temperature and pressure sensed by a thermostatic expansion sensor placed in the low pressure circuit. Flow of the refrigerant into the heat exchanger may be reduced where the sensed pressure or temperature indicates the risk of refrigerant in the liquid state entering the compressor. A liquid suction heat exchanger, as would be known to one skilled in the art, is used to transfer heat from refrigerant in the high pressure circuit to the refrigerant in the low pressure circuit to heat the low pressure refrigerant and reduce the risk of refrigerant in the liquid state entering the compressor while increasing the subcooling of the high pressure refrigerant. However, as would be understood to one skilled in the art, the invention is not limited to any one heat exchanger but any suitable heat exchanger may be used.
In the operation of a preferred embodiment, according to the inventive principles, ambient air through the return duct or fresh outside air, or a mixture of returned and outside air, is introduced into the air conditioning system and directed over the air conditioning refrigeration equipment""s evaporator coil heat exchanger or the heat exchanger in a chilled liquid system, for example, and into a bypass duct or passage extending around the conditioning refrigeration equipment. An output mixing plenum for mixing air flowing from the air conditioning equipment""s heat exchanger with the air flowing from the bypass duct or passage, is located downstream of the bypass duct and the air conditioning refrigeration equipment. A fan(s) is placed to move air into the bypass duct and over the air conditioning equipment, and a damper regulates the flow of air into the bypass duct relative to the flow of air through the heat exchanger. According to the inventive principles as disclosed in connection with the preferred embodiment, the fan(s) may be single, staged, variable or multi speed.
As stated above and according to the inventive principles as disclosed in connection with the preferred embodiment, control over the level of humidity is achieved independently of temperature by the operation of the system to cool some of the intake air drawn into the system while directing the other part of the intake air around the air conditioning heat exchanger through a bypass duct. The amount of air directed through the air conditioning, relative to the amount of air directed through the bypass, is regulated so the air directed into the output mixing plenum from the air conditioning equipment and the bypass duct will provide a comfortable temperature within the setting of the temperature control while the humidity is reduced to a level within the setting of the independent humidity control. An air flow regulation means is used to vary the operation of the conditioning means by adjusting the air flow to provide a relatively high level of air flow through the bypass duct or passage in relation to the air flow through the air conditioning means. In this way, the air from the air conditioner means is mixed with the air to the bypass to reduce the temperature of the bypassed air and reduce its humidity, which is then directed to a controlled space where it is mixed again with ambient air and raised to a desired temperature level and reduced humidity level. The reduction in humidity is achieved by the passage of air through the air conditioning heat exchanger. The relative humidity of the ambient air through the bypass is reduced when mixed with the air cooled and dehumidified by the air conditioner hear exchanger. At the same time, the temperature of the air-conditioned dehumidified air is raised. Then the mixed air from the mixing chamber is introduced into the controlled space, reducing the relative humidity in the controlled space. Where required to provide relatively high levels of air cooling in relation to air dehumidification in order to satisfy user set points and maximize energy efficiency, the system control and regulation means varies operation of the conditioning means while setting the airflow regulation means to a state providing a relatively low level of air flow through the bypass duct or passage in relation to the air flow through the conditioning means. In systems that use a dual or multiple speed blower(s), a lower blower speed is selected when the airflow regulation means provides higher levels of airflow through the bypass duct to assist in the process.
As stated above and according to the inventive principles as disclosed in connection with the preferred embodiment, liquid refrigerant is prevented from entering the compressor, of concern when the airflow through the bypass duct is increased and the airflow through the air conditioning equipment is reduced. According to the inventive principles, an adjustable or electronic thermostatic refrigerant expansion valve (TXV) is used to ensure that the refrigerant is fully evaporated upon exiting the evaporator heat exchanger coil. A liquid-suction heat exchanger is used to provide subcooling of the refrigerant as it flows from the condenser to the expansion valve and superheating of the refrigerant as it flows from the evaporator heat exchanger to the compressor. To prevent the accumulation of ice on the evaporator heat exchanger coil, the controller responds to the temperature of the coil to vary the operation of the air conditioning equipment, fan and/or airflow regulation means.
In summary, using known systems the removal of heat for the sole purpose of dehumidification was not possible with systems relying upon existing temperature-based humidity controls or comfort range controllers. In these systems excessive overcooling of the space and/or equipment failure would occur, requiring energy expensive reheat or additional costly components. With the invention, which functions as a system, more dehumidification is provided with little or no overcooling and reheating. This reduces or eliminates the need to overcool and then reheat or rely upon a comfort-zone temperature and humidity combination since temperature and humidity are user selectable and controlled separately. The invention provides independent humidity control while preserving as much sensible heat as possible from the inlet air when needed, thus limiting sensible cooling relative to latent cooling without using reheat or additional coils, thereby maximizing energy efficiency.